What is the difference between --save and --save-dev?

Question

What is the difference between:

npm install [package_name]

and:

npm install [package_name] --save

and:

Answer 1

As suggested by @andreas-hultgren in this answer and according to the npm docs:

If someone is planning on downloading and using your module in their program, then they probably don't want or need to download and build the external test or documentation framework that you use.

However, for webapp development, Yeoman (a scaffolding tool that installs a peer-reviewed, pre-written package.json file amongst other things) places all packages in devDependencies and nothing in dependencies, so it appears that the use of --save-dev is a safe bet in webapp development, at least.